The methods of water disinfection most frequently used, and the art of water treatment in general, is most often represented by various hydro-separators, clarifiers, mechanical filters, and/or chemically oriented apparatus and flocculation/coagulation procedures (including chemical post-treatment) whereby impurities are removed from water. The basic types of known water treatment purification arrangements and their accompanying problems and limitations may be categorized generally as follows:
1. Non-regeneratable modular filters are one time use, short-term devices of inexpensive cartridge design that have restrictive low-flow and high head-loss pressure limitations. Typical filter materials are packed cellulose or fibrous/filament textiles that, at best, provide (at optimal flow) no better than a continuous 5–10 micron absolute particle size separation or filtration. Minor recognizable suspended solids in the water influent flow will quickly clog the filter media material within the cartridge and render the filter system involved inoperable. Where moderate and high flow rates are involved, replacement costs and down time are inordinately costly and burdensome. These canister/cartridge filters and separation units are usually non-compatible and fairly short-lived if exposed to oxidizing and corrosive chemical treatment agents within the contaminated water to be purified.
2. Chemical treatment methods typically include use of oxidizers, polymers, flocculants, and/or coagulants, and may also include use of chlorine for disinfection and sterilization. These methods are cost prohibitive and labor-intensive and can require high maintenance, as they can damage the associated waste treatment equipment component(s) system. Further, various chemical treatments involve health and safety risks leading to restrictions on their use and reduction of permitted exposure. Commonly, chemical process treatment methods lead to the generation of voluminous amounts of toxic chemical solids and sludges along with the associated environmental exposure liability problems; further, these methods may involve liability issues and regulatory agency controls due to the necessity of disposal of these hazardous substances.
3. Ozone generators, e.g., as conventionally offered as “Corona-Arc Generation” disinfection and treatment systems provide a high voltage electric arc or corona. These open spark discharges are conducive to potentially dangerous situations. Moreover, these systems require fairly high power and have relatively high maintenance requirements, and are expensive to operate in that they require a supply of low-humidity air (leading to continuous desiccator and dryer maintenance requirements) and further require high maintenance air-separation oxygen concentrator equipment. Problems due to potentially toxic exposure to ozone can also exist.
4. Reverse osmosis (R. O.) treatment systems, involving membrane separation of sub-micron particles from water, often present problems associated with shortened membrane life due to plugging, limited process flow capacity, and disinfection of the membrane so as to be free from contaminating biological agents and/or oily materials. The R.O. membrane is highly susceptible to fouling with biological growth; further, R.O. treatment systems are costly both as to initial cost and in operation, as they require substantial electrical power to provide the high pressure needed for operation, and due to their high maintenance requirements.
5. Traditional filtration systems employ one or more of carbon, anthracite, coal, paper, fibrous materials, “mixed media”, and/or sand as a physical removal method, that is, to establish a solids separation and filtration process. These systems often involve operational problems such as early fouling of the filtration media, which often requires very frequent filter back-washing and adds difficulties relative to the disposal of large quantities of the backwashed materials. The back-wash water may be very biologically active and also require disinfection, due to “bleed through” bacterial recontamination of the water being treated. Quite often, in order to maintain a steady-state level of solids removal and continuous purification efficiencies, the entire volume of filtration materials must be removed and replaced several times per year due to encrustment and contamination.
6. Ion exchange filters basically remove only dissolved ions and electrically charged colloidal solids; they rapidly plug in the presence of suspended solids. Even a moderate flow (50–100 GPM) ion exchange filter system represents a complex plumbing network involving unwieldy resin filter and/or “zeolite staged” containers and requires large regenerative acid and base tankage. Regeneration of the filter resin is complicated and is often incomplete due to the plugging of the resin pore spaces by the larger particle size suspended solids that gain entry into the flow. These systems have substantial flow rate restrictions limiting their practicality for larger commercial or general-purpose use. Thus, ion exchange filtration is suitable only for very select water treatment or specific wastewaters and also often involves high capital equipment purchase cost in addition to high repetitive media replacement and operational costs.